Test APIs & Isolation

Unlike traditional emulator-based Android tests, Robolectric tests run inside a sandbox which allows allows the Android environment to be precisely configured to the desired conditions for each test, isolates each test from its neighbors, and extends the Android framework with test APIs which provide minute control over the Android framework’s behavior and visibility of state for assertions.

While much of the Android framework will work as expected inside a Robolectric test, some Android components’ regular behavior doesn’t translate well to unit tests: hardware sensors need to be simulated, system services need to be loaded with test fixture data. In those cases, Robolectric provides a test double that’s suitable for most unit testing scenarios.

Run Tests Outside of the Emulator

Robolectric lets you run your tests on your workstation, or on your continuous integration environment in a regular JVM, without an emulator. Because of this, the dexing, packaging, and installing-on-the emulator steps aren’t necessary, reducing test cycles from minutes to seconds so you can iterate quickly and refactor your code with confidence.

SDK, Resources, & Native Method Simulation

Robolectric handles inflation of views, resource loading, and lots of other stuff that’s implemented in native C code on Android devices. This allows tests to do most things you could do on a real device. It’s easy to provide your own implementation for specific SDK methods too, so you could simulate error conditions or real-world sensor behavior, for example.

No Mocking Frameworks Required

An alternate approach to Robolectric is to use mock frameworks such as Mockito or to mock out the Android SDK. While this is a valid approach, it often yields tests that are essentially reverse implementations of the application code.

Robolectric allows a test style that is closer to black box testing, making the tests more effective for refactoring and allowing the tests to focus on the behavior of the application instead of the implementation of Android. You can still use a mocking framework along with Robolectric if you like.